Recently, magnetic recording media with higher coercive forces have come into use as magnetic recording/reproducing devices become downsized and obtain higher capacities. As a magnetic head for high-density magnetic recording which has a sufficient capability of writing signals on such media, a metal-in-gap (MIG) head has been developed. The MIG head is a type of magnetic head in which gap opposing surfaces of a magnetic core halves are deposited with a metal magnetic film having a high saturation flux density (for example, thin films of magnetic metal materials (hereinafter abbreviated as metal magnetic film) such as Fe—Ta—N, Fe—Ta—Si—N, Fe—Nb—N, Fe—Nb—Si—B—N, Fe—Ta—C, Co—Ta—Zr—Nb, or Co—Nb—Zr—N), and then brought into abutment with each other via a magnetic gap material to be bonded with sealing glass. Conventional magnetic substances such as permalloy (Fe—Ni alloy) and Sendust (Fe—Al—Si alloy) have a relatively low saturation flux density and therefore cannot be used as the metal magnetic film of a high performance MIG head.
The structure of a MIG head is shown in FIG. 1. Metal magnetic films 3, 4 having a high saturation flux density are formed on magnetic gap opposing surfaces of magnetic core halves 1, 2 made of ferrite. The magnetic gap opposing surfaces are brought into abutment with each other via a magnetic gap material 5 and then secured with sealing glass 6, 7.
A MIG head is fabricated in a process as outlined in FIG. 2. First, a winding groove 8 and a glass groove 9 are formed on a pair of magnetic core halves 1, 2(a). Then, a truck groove 10 to define the truck width is formed (b). Further, metal magnetic films 3, 4 (not shown) are deposited on the ground magnetic gap opposing surfaces, and on top of which a magnetic gap material 5 (not shown) is deposited. Thereafter, magnetic gap opposing surfaces are abutted with each other and sealing glass 6, 7 are disposed in the front gap and the back gap respectively (c), and the pair of the core halves are bonded by heat treatment (d). Thus, a magnetic core block formed by bonding the magnetic core halves by molding sealing glass is cut to a predetermined size and ground to fabricate a magnetic head chip 11(e). This magnetic chip undergoes processes such as base bonding and wire winding to be completed as a magnetic head.
The bonding by means of sealing glass is carried out by softening, cooling, and solidifying the glass by a suitable heat treatment. During this process, to prevent thermal degradation of components such as the above described metal magnetic film, it is necessary to select sealing glass which can be used at temperatures not exceeding the heat resistant temperatures of those components. For a MIG head, it is necessary to use sealing glass which can be used in a low-temperature heat treatment not higher than 600 degrees C.
Generally, when bonding is carried out by softening and fluidizing glass by heating, an actual heat treatment is conducted at a temperature called a working point of the sealing glass to be used. Therefore, for MIG heads, sealing glass of which working point is not higher than 600 degrees C. is used. Here, the working point of glass is a characteristic temperature at which the viscosity of the glass reaches 103 Pa·s thus fluidizing the glass.
However, sealing glass with a working point exceeding the heat resistant temperatures of the components of the magnetic head can be used as long as the original purpose that is to bond a pair of ferrite cores to fabricate the magnetic head is accomplished. For example, when molding is conducted by squeezing glass under pressure in a high viscosity state, sealing glass with a high working point may be used.
From the above described reason, sealing glass with an associated working point not higher than 650 degrees C. is desired for a MIG head. Sealing glass having such a low working point has been developed, which includes SiO2—B2O3—PbO glass systems and B203—PbO—ZnO glass systems, and lead glass primarily composed of lead oxides (for example, see Japanese Patent Laid-Open No. 7-161011).
As demands for high performance, high reliability magnetic recording/reproducing devices increase recently, further development of magnetic heads with a higher record density and higher durability are desired. To cope with higher record densities, it is necessary to realize a magnetic head having a metal magnetic film having a high saturation flux density and a structure of a narrower truck width.
As an alloy film of a high saturation flux density suitable for high-density recording, an alloy TaMbXcNd is proposed, for example, in Japanese Patent Laid-Open No. 2-208811. In the formula, T is at least one kind of metal selected from the group consisting of Fe, Co, and Ni; M is at least one kind of metal selected from the group consisting of Nb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X is at least one kind of half metal/semiconductor selected from the group consisting of B, Si, and Ge; N is nitrogen; and a, b, c, and d represent atomic percent where 65≦a≦93, 4≦b≦20, 1≦c≦20, 2≦d≦20, and a+b+c+d=100.
Furthermore, a TaMbXcAd alloy film which includes alloys other than the above described TaMbXcNd alloy has a high saturation flux density and is therefore suitable for high-density recording. In the formula, T is at least one kind of metal selected from the group consisting of Fe, Co, and Ni; M is at least one kind of metal selected from the group consisting of Nb, Zr, Ti, Ta, Hf, Cr, Mo, W, and Mn; X is at least one kind of half metal/semiconductor selected from the group consisting of B, Si, and Ge; A is N or C; and a, b, c, and d represent atomic percent where 65≦a≦93, 4≦b≦20, 0≦c≦20, 2≦d≦20, and a+b+c+d=100.
To accomplish a magnetic head suitable for high-density recording, a structure with a narrower truck width is also needed. To maintain the strength of such a magnetic head, it is necessary to enhance the strength of the sealing glass that serves to bond the ferrite cores. Also, since the sealing glass occupies a relatively larger area in the sliding surface of the magnetic head, the sealing glass is prone to wear during the movement of the magnetic recording medium. Therefore, it is important for sealing glass for high performance magnetic heads to have a high strength, and high wear resistance of the sliding surface.
However, there was a problem with conventional sealing glasses in that they lack mechanical strength; for example, they are susceptible to wear on the sliding surface, or prone to be fractured or chipped. For example, Japanese Patent Laid-Open No. 7-161011 discloses an embodiment of sealing glass composed of 9.9 wt % of SiO2, 12.2 wt % of B2O3, 70.2 wt % of PbO, 1.6 wt % of Al2O3, 4.5 wt % of ZnO, and 1.3 wt % of Na2O. However the magnetic head fabricated by using this sealing glass was found to have severe wear in the sealing glass or fractures in the magnetic head.